treasure chest

plural treasure chests

1. A chest filled with treasure, especially one used by pirates, etc.
2. metonymicallyA treasury, especially a state or royal treasury.

   The visitors pour upward of $60,000 into the state’s treasure chest.

   1977, Richard Hyatt, The Carters of Plains, page 103

   2 more examples

   They acted the part of a sponge for the Royal Treasury, they gathered up all the floating money of the country, to be squeezed from time to time into the king’s treasure-chest […]

   1892, Joseph Jacobs, “Notes on the Jews of England under the Angevin Kings”, in The Jewish Quarterly Review, volume 4, page 634

   When Anglo-Saxon coins left England for Scandinavia they could, hypothetically, have been withdrawn from a royal treasure-chest replenished from tolls and taxes collected nationwide.

   2006, D. M. Metcalf, “Inflows of Anglo-Saxon and German coins into the Northern lands c. 997–1024: discerning the patterns”, in Barrie Cook, Gareth Williams, editors, Coinage and History in the North Sea World, c. AD 500–1250, →ISBN, page 364

3. figurativelyAny source of something valuable or beautiful.

   a treasure chest of poems

   Synonyms: gold mine, treasure trove